All Discussions Tagged 'effect' - Home Energy Pros2015-03-03T19:32:14Zhttp://homeenergypros.lbl.gov/forum/topic/listForTag?tag=effect&feed=yes&xn_auth=noAre "Stack Effect" and "Chimney Draft" the same?tag:homeenergypros.lbl.gov,2013-11-08:6069565:Topic:1404622013-11-08T15:31:49.599ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>A year plus ago J Brooks asked a question, "I am curious if you have found any references for the origin of the term "Stack Effect"? Is it named after Chimney Stack or is Chimney Stack named <strong>after</strong> Stack Effect?" post 60 <a href="http://www.greenbuildingadvisor.com/community/forum/general-questions/23103/what-must-we-say?page=1">http://www.greenbuildingadvisor.com/community/forum/general-questions/23103/what-must-we-say?page=1</a></p>
<p>The actual origin is only a…</p>
<p>A year plus ago J Brooks asked a question, "I am curious if you have found any references for the origin of the term "Stack Effect"? Is it named after Chimney Stack or is Chimney Stack named <strong>after</strong> Stack Effect?" post 60 <a href="http://www.greenbuildingadvisor.com/community/forum/general-questions/23103/what-must-we-say?page=1">http://www.greenbuildingadvisor.com/community/forum/general-questions/23103/what-must-we-say?page=1</a></p>
<p>The actual origin is only a curiosity, but there is a difference between house stack effect (HSE) and chimney stack effect (CSE) and understanding that difference may help in other applications. I'll be brief.</p>
<p>Consider a tall house with only two 6" holes, one top and one bottom. House is warm and it is cold outside. The HSE pressure will be divided approximately half high and half low resulting is an inflow at the bottom opening matched by an outflow at the upper opening, each the result of half of the HSE pressure across a 6" opening.</p>
<p>Now, shrink that house down to 6" in diameter, in other words, a chimney. Keep the temperatures and height the same and you will have the same total HSE pressure now equal to the CSE. But the total pressure no longer divides equally between the upper opening and the lower opening. The difference between a chimney and a house is that the air remains in motion where in a house, once it enters it loses its momentum and communicates with the top opening via an increased pressure. The air flow through the chimney is subject to the full SE pressure where the air flow through the house it is only half the pressure. Other resistances play into the actual air flow, but a chimney chase may experience a greater air flow because the momentum of the air is maintained. </p>
<p>So, where did the name come from? Despite their similarities, chimney draft and HSE are actually different. Neither one should be named after the other. (IMO)</p>
<p>Bud</p> Hot air languagetag:homeenergypros.lbl.gov,2013-09-28:6069565:Topic:1387362013-09-28T22:49:47.483ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>One of the objectives of my many discussions on "why hot air rises" has been to change the way we describe that process. The reason I believe that change is needed is the current simplified description has inadvertently credited hot air with its own mystical power to levitate itself, which of course it doesn't have.</p>
<p>In place of phrases like "the warm air rises" it is better to say "the warm air is pushed up". Saying "it rises" implies it does so on its own, where saying "it is…</p>
<p>One of the objectives of my many discussions on "why hot air rises" has been to change the way we describe that process. The reason I believe that change is needed is the current simplified description has inadvertently credited hot air with its own mystical power to levitate itself, which of course it doesn't have.</p>
<p>In place of phrases like "the warm air rises" it is better to say "the warm air is pushed up". Saying "it rises" implies it does so on its own, where saying "it is pushed up" clearly states that another force is responsible for the upward air flow. In most cases, that other force is the colder air to which it is being compared.</p>
<p>So, why the fuss, the wording doesn't seem to be all that different? When talking to home owners, simplicity is often the better choice. But when discussing air flow with those trained in home performance along with the HVAC and other related technical people, it is desirable to perpetuate the correct explanation. Here are some examples of what has evolved from the current poor choice of wording.</p>
<p>1. The "short circuit" issue often discussed in relation to gable vents "short circuiting" the air flow between soffit and ridge vents is incorrect. Air will continue to flow into the soffit vents based upon the pressure difference between inside and outside. There are reasons to close off the old gable vents, weather, lack of air sealing, but the short circuit reasoning is wrong. If they have to be removed, do it for the right reason. Otherwise, save the homeowner some money and gain the benefits of extra ventilation.</p>
<p>2. The warm/hot air flowing upward through a chimney is not pulling its replacement air into the combustion appliance from which it originated. It is the heavier air surrounding that appliance that is pushing the warm air up the chimney and providing the necessary supply of combustion air.</p>
<p>3. Advising someone to open a window to facilitate starting a fire in a wood stove or fireplace can be dangerous advice. Understanding the effect of opening that window (shifting the neutral plane) will help explain why they should be looking for another solution, like a dedicated direct air source. </p>
<p>4. If hot air is not rising by itself to exit through high leaks and thus not pulling in colder air through lower leaks, how would you explain stack effect? I'll let you work on that one.</p>
<p>Why hot air moves up is a simple principle and one that can help all of us sort out some very complex problems. </p>
<p>The selected examples above come with longer explanations which we can cover as needed.</p>
<p>Bud</p>